(1) Field of the Invention
The present invention belongs to a fluid flow rate detection technology, and particularly relates to a flow rate sensor for detecting the flow rate of fluid flowing in a pipe line. The present invention intends to enhance the detecting accuracy of the flow rate sensor.
Further, the present invention relates to a strainer-integrated portable flowmeter which can be mounted on a pipe line through which kerosene is supplied to a kerosene burning apparatus such as a stove, boiler or the like to measure the flow rate of kerosene while removing a foreign matters such as dust or the like.
(2) Description of the Related Art
Various types of sensors have been hitherto used as a flow rate sensor (or flow velocity sensor) for measuring the flow rate (or flow velocity) of various fluid, particularly liquid, and a so-called thermal (particularly indirectly heated type) flow rate sensor is used because the cost can be easily reduced.
A sensor in which a thin-film heating element and a thin-film temperature sensing element are laminated through an insulating layer on a substrate and the substrate and the fluid in the pipe line are thermally connected to each other is used as an indirectly heated type flow rate sensor. By passing current through the heating element, the temperature sensing element is heated to vary the electrical characteristic of the temperature sensing element such as the value of the electrical resistance of the temperature sensing element. The electrical resistance value (varied on the basis of the temperature increase of the temperature sensing element) is varied in accordance with the flow rate (flow velocity) of fluid flowing in the pipe line. This is because a part of the heating value of the heating element is transferred through the substrate into the fluid, the heating value diffusing into the fluid is varied in accordance with the flow rate (flow velocity) of the fluid, and the heating value to be supplied to the temperature sensing element is varied in accordance with the variation of the heating value diffusing into the fluid, so that the electrical resistance value of the temperature sensing element is varied. The variation of the electrical resistance value of the temperature sensing element is also varied in accordance with the temperature of the fluid. Therefore, a temperature sensing device for temperature compensation is installed in an electrical circuit for measuring the variation of the electrical resistance value of the temperature sensing element to suppress the variation of the flow-rate measurement value due to the temperature of the fluid at maximum.
An indirectly heated type flow rate sensor using thin film elements as described above is disclosed in JP-08-146026(A), for example.
The conventional indirectly heated type flow rate sensor is secured to a linear pipe line portion so that the substrate of a flow rate detector or a casing which is thermally connected to the substrate is exposed from the wall surface of the pipe line to the fluid.
When the fluid is viscous fluid, particularly liquid, the flow-velocity distribution on the section perpendicular to the flow of the fluid in the pipe line becomes ununiform (there is a great difference in flow velocity between the center portion and the outer peripheral portion on the section). In the case of the conventional sensor in which the substrate or the casing portion connected to the substrate is merely exposed to the fluid at the wall of the pipe line, the flow-velocity distribution has a great effect on the precision of the flow-rate measurement. This is because the flow velocity of the fluid flowing at the center portion on the section of the pipe line is not taken into consideration, but only the flow velocity of the fluid in the neighborhood of the wall of the pipe line is taken into consideration. As described above, the conventional flow rate sensor has such a problem that it is difficult to measure the flow rate of fluid accurately when the fluid is viscous fluid. Even when fluid has low viscosity at room temperature, it induces a problem connected to the above viscosity problem because the viscosity of the fluid increases as the temperature is lowered.
The flow rate sensor is required to be used under an extremely broad temperature environment in accordance with a geographical condition, an indoor or outdoor condition, etc. Further, these conditions are added with a season condition, a day or night condition, etc., and the temperature environment is greatly varied. Therefore, there has been required a flow rate sensor which can detect the flow rate accurately under such a broad environmental temperature condition as described above.
As mentioned in the above, the temperature sensing device for temperature compensation is installed in the measuring electrical circuit. However, it is insufficient for suppressing the variation of the flow-rate measurement value due to the temperature of the fluid. Accordingly, it is required to furthermore reduce the temperature dependence of the detected flow rate value to enhance the detecting precision.
Therefore, an object of the present invention is to provide a flow rate sensor which can accurately measure the flow rate of fluid flowing in a pipe line even when the fluid is viscous fluid.
Further, an object of the present invention is to provide a flow rate sensor which can accurately measure the flow rate of the viscous fluid flowing in a pipe line under a broad environmental temperature condition on the basis of lowering the temperature dependence of the detected flow rate value.
Further, a kerosene burning apparatus such as a stove, boiler or the like burns kerosene and produces heat to increase the temperature of air and heat the inside of a room, to heat and boil a large amount of water and to produce high-pressure steam serving as a driving source.
In a boiler 401 shown in FIGS. 27, 28A and 28B, kerosene is supplied from a tank 402 through a pipe line 403, and then burned by a burner 404 while sprayed. By using heat produced at this time, a large amount of water is boiled or high-pressure steam is produced, and the combustion gas is discharged from a funnel 405.
Further, a strainer 407 for removing foreign matter such as dust, motes, etc. is disposed between the tank 402 and the pump 406, and a flowmeter 408 for measuring the flow rate of kerosene is disposed between the pump 406 and the burner 404.
However, when minute foreign matters passing through the strainer 407 are gradually accumulated or foreign matters invade between the strainer 407 and the burner 404, these foreign matters cannot be removed and the foreign matters invade into the nozzle 409 of the burner 404, thereby closing a part of the discharge port 409a. 
In such a case, the amount of kerosene passing through the nozzle 409 is reduced and thus the burner 404 cannot exhibit its sufficient performance, resulting in reduction of the heat value produced in the boiler 401. Further, since kerosene is incompletely burned (combusted), the energy held by the kerosene is vainly dissipated to produce incomplete combustion gas such as carbon monoxide or the like, which causes air pollution.
In order to solve the above problem, there has been proposed an air fuel ratio control method for measuring the flow rate of kerosene flowing in a pipe line 403 with a flowmeter 408 disposed in the pipe line and supplying a suitably amount of air corresponding to the measurement value to burn kerosene.
According to this method, even when a part of the discharge port 409a of the nozzle 409 is closed, no incomplete combustion occurs and thus the vain consumption of the holding energy of kerosene and the air pollution due to the incomplete combustion can be prevented. If the foreign matters in the nozzle 409 is jetted from the discharged port 409a under jetting pressure of kerosene or the like, the burner 404 can exhibits its inherent performance and the heating value of the boiler 401 is restored to its normal value.
When conducting the air fuel ratio control method, it is necessary to detect the flow rate of the kerosene flowing through the pipe line 403 by means of the flowmeter 408 disposed in the pipe line. However, since the flowmeter 408 is disposed downstream away from the strainer 407 with a considerable interval, the minute foreign matters passed through the strainer 407 is accummulated, and the foreign matters invades the pile line between the strainer 407 and the flowmeter 408. When these foreign matters invades the inside of the flowmeter 408 to be fixed to and accummulated on O-ring at the sensor mount portion for example, a gap is formed there to cause leak of the kerosene. If the foregn matters are fixed to and accummulated on the fin plate of the sensor, an area of the fin plate used for heat conduction is reduced and a detail of the kerosene flow around the fin plate is changed to thereby cause significant lowering of the detection accuracy of the flowmeter.
In such cases, it is necessary to remove the flowmeter 408 from the pipe line, perform cleaning treatment of the flowmeter 408 or change the defective parts to a fresh one, and then attach the flowmeter 408 to the pipe line again. However, air remains in the pipe line when the flowmeter 408 is attached thereto again, and therefore air bubbles are formed to remain in the pipe line at the upper side thereof if the kerosene is flown in the pipe line. If the air bubbles are fixed to the heat transfer member of the sensor, the heat transferring manner through the heat transfer member is changed to cause significant lowering of the detection accuracy of the flowmeter 408.
According to the air fuel ratio control method, the incomplete combustion can be prevented, however, the reduction of the heating value produced in the boiler 301 cannot be prevented. Further, if foreign matters in the nozzle 309 are not discharged from the discharge port 309a, they must be artificially removed. However, in the conventional flowmeter 408, an operator cannot recognize the flow rate of the kerosene directly so that the operation al work of removing the foreign matters from the inside of the nozzle 409 cannot be conducted immediately.
The present invention has been implemented to solve the above problems, and has an object to provide a strainer integrated flowmeter which is hardly invaded by the foreign matters, does not permit the remaining of the air in the pipe line, can measure the flow rate of fluid such as kerosene passing through the pipe line accurately over long duration, and make it possible for the operator to recognize the flow rate of the fluid such as kerosene directly.
In order to attain the above object, according to the present invention, there is provided a strainer integrated flowmeter comprising a strainer section provided with a housing having a flow passage formed therein, a filter member and a filter member insertion cylinder; and a flowmeter section provided with a housing having a flow passage formed therein and a flow rate sensor, wherein the housing of the strainer section and the housing of the flowmeter section are integrated, and the flowmeter section is disposed downstream the strainer section.
In order to prevent the air bubbles from remaining at the upper side of the flow passage, it is preferable to form a vent hole in the integrated housing so as to be in communication with the flow passage formed in the integrated housing.
In order for the operator to immediately recognize the flow rate value of the fluid such as kerosene, it is preferable that the flowmeter section is provided with a display portion for indicating a flow rate value, an operating portion for supplying electric power and detecting a flow rate, and an electric circuit for driving the display portion to indicate the flow rate value detected by the flow rate sensor.
In order to perform highly sensitive flow rate detection, it is preferable that the flow rate sensor comprises a flow rate detector having a heating element and a temperature sensing element both formed on a substrate; a fin plate through which heat is transferred to/from a fluid; and an output terminal for outputting a voltage value corresponding to the flow rate, and, said flow rate detector, a portion of the fin plate and a portion of the output terminal are sealed with molding.
In order to reduce the error in the detected flow rate value due to the temperature of the fluid such as kerosene, it is preferable that the flowmeter section is provided with a temperature sensor for detecting a temperature of fluid.
In order to perform highly sensitive temperature detection, it is preferable that the temperature sensor comprises a temperature detector having a temperature sensing element formed on a substrate; a temperature sensor fin plate through which heat is transferred to/from said fluid; and a temperature sensor output terminal for outputting a voltage value corresponding to the temperature, and, the temperature detector, a portion of the temperature sensor fin plate and a portion of the temperature sensor output terminal are sealed with molding.
The detected flow rate value can be indicated digitally on the display portion in case that the electric circuit comprises the temperature sensing element of the flow rate sensor, the temperature sensing element of the temperature sensor, and a bridge circuit which output a voltage difference corresponding to the flow rate of the fluid, wherein the electric circuit further comprises a V/F conversion circuit for converting the voltage difference corresponding to the flow rate of the fluid to a pulse signal having corresponding frequency, a counter for counting number of pulse of the pulse signal, and a microcomputer for converting output of the counter to a flow rate value corresponding to the frequency.
According to the present invention, in order to attain the above object, there is provided a flow rate sensor comprising a flow rate detector having a heating function and temperature sensing function; a fluid-flowing pipe line for a fluid to be detected; and a flow rate detecting heat transfer member disposed so as to be affected by a heat generated in the flow rate detector and extend into the inside of the pipe line, wherein temperature sensing which is affected by a heat absorption effect of the fluid due to the heat through the flow rate detecting heat transfer member is executed in the flow rate detector, and a flow rate of the fluid in the pipe line is detected on the basis of result of the temperature sensing, wherein the pipe line has a fluid inflow side portion, a fluid out flow side portion and a center portion positioned between the fluid inflow side portion and fluid outflow side portion, the flow rate detecting heat transfer member extends into the inside of the pipe line at the center portion, and an inner diameter of the center portion is smaller than that of the fluid inflow side portion.
In an aspect of the invention, the inner diameter of the center portion is 50-80% of the inner diameter of the fluid inflow side portion.
In an aspect of the invention, the inner diameter of the fluid outflow side portion is substantially equal to the inner diameter of the fluid inflow side portion.
In an aspect of the invention, an intermediate portion is formed between the center portion and the fluid inflow side portion, the intermediate portion having a continuously varying inner diameter and a length of a half or less of a difference between the inner diameter of the fluid inflow side portion and the inner diameter of the center portion.
In an aspect of the invention, the flow rate detecting heat transfer member is disposed at a position separated from a fluid inflow side edge of the center portion by 4 times or less of the inner diameter of the center portion.
In an aspect of the invention, the flow rate detector comprises a thin-film heating element and a flow rate detecting thin-film temperature sensing element disposed so as to be affected by the effect of the heating of said thin-film heating element, the thin-film heating element and the flow rate detecting thin-film temperature sensing element being formed on the flow rate detecting heat transfer member at an outside of the pipe line.
In an aspect of the invention, the flow rate detecting heat transfer member has a shape of plate and is arranged in parallel to a fluid-flowing direction in the pipe line.
In an aspect of the invention, the flow rate sensor further comprises a fluid temperature detector for use in thermal compensation of flow rate detection, and a fluid temperature detecting heat transfer member extending into the inside of the pipe line, wherein the fluid temperature detector and the fluid temperature detecting heat transfer member are thermally connected to each other.
In an aspect of the invention, the fluid temperature detecting heat transfer member is disposed in the center portion of the pipe line at a fluid outflow side of the flow rate detecting heat transfer member.
In an aspect of the invention, the fluid temperature detecting heat transfer member has a shape of plate and is arranged in parallel to a fluid-flowing direction in the pipe line.
According to the present invention, in order to attain the above object, there is provided a flow rate sensor comprising a flow rate detector having a heating function and temperature sensing function; a fluid-flowing pipe line for a fluid to be detected; and a flow rate detecting heat transfer member disposed so as to be affected by a heat generated in the flow rate detector and extend into the inside of the pipe line, wherein temperature sensing which is affected by a heat absorption effect of the fluid due to the heat through the flow rate detecting heat transfer member is executed in the flow rate detector, and a flow rate of the fluid in the pipe line is detected on the basis of result of the temperature sensing, wherein the flow rate detecting heat transfer member is exposed to an inside of the pipe line only at a central area located from a center line of the pipe line to a radial position of 80% or less of a radial interval between the center line and an inner surface of the pipe line.
In an aspect of the invention, the flow rate detecting heat transfer member extends into the pipe line in a radial direction thereof so that a tip end thereof is positioned in the central area, and a base of a portion of the flow rate detecting heat transfer member which is disposed in the pipe line but outside the central area is sealed with a heat insulation member.
In an aspect of the invention, the flow rate detector and a portion of the flow rate detecting heat transfer member thermally connected to the flow rate detector are accommodated within a base portion having heat insulation property, and the heat insulation member is constituted by a part of the base portion.
In an aspect of the invention, the base portion and the heat insulation member are made of synthetic resin.
In an aspect of the invention, the flow rate detector comprises a thin-film heating element and a flow rate detecting thin-film temperature sensing element disposed so as to be affected by the effect of the heating of the thin-film heating element, said thin-film heating element and a flow rate detecting thin-film temperature sensing element being formed on the flow rate detecting heat transfer member at an outside of the pipe line.
In an aspect of the invention, the flow rate detecting heat transfer member has a shape of plate and is arranged in the pipe line along a direction thereof.
In an aspect of the invention, the flow rate sensor further comprises a fluid temperature detector for use in thermal compensation of flow rate detection, and a fluid temperature detecting heat transfer member extending into the inside of the pipe line, wherein the fluid temperature detector and the fluid temperature detecting heat transfer member are thermally connected to each other.
In an aspect of the invention, the temperature detecting heat transfer member is exposed to the inside of the pipe line only at the central area.
In an aspect of the invention, the temperature detecting heat transfer member extends into the pipe line in a radial direction thereof so that a tip end thereof is positioned in the central area, and a base of a portion of the temperature detecting heat transfer member which is disposed in the pipe line but outside the central area is sealed with a heat insulation member.
In an aspect of the invention, the temperature detector and a portion of the temperature detecting heat transfer member thermally connected to the temperature detector are accommodated within a base portion having heat insulation property, and the heat insulation member is constituted by a part of the base portion.
In an aspect of the invention, the temperature detecting heat transfer member has a shape of plate and is arranged in the pipe line along a direction thereof.